Sunday, December 27, 2015

Rapid pollutant detection can prevent widespread outbreaks. While many techniques exist for detecting such contamination, they generally require highly specific instruments for each contaminant. Peter Vikesland, professor of civil and environmental engineering at Virginia Tech, and Haoran Wei of Zaozhuang in Shandong, China, a doctoral student in environmental engineering, describe challenges related to deploying surface-enhanced Raman spectroscopy (SERS) for detection in their paper published by Scientific Reports, “pH-Triggered Molecular Alignment for Reproducible SERS Detection via an AuNP/Nanocellulose Platform.”

SERS has great potential for ultrasensitive chemical analysis and detection of multiple contaminants in a range of environments. Capable of detecting single molecules without excessively expensive equipment or sample pretreatment, SERS has promised rapid field and point-of-use detection that could prevent pollution or biohazard threats and stop outbreaks before they begin. But that promise has gone largely unfulfilled.

One problem is that many of the substances that SERS could potentially detect are moderately hydrophobic, or water-repellent, thus making it harder to attract them to the hydrophilic, or water-loving, gold or silver nanoparticle surfaces used for SERS. Efforts to use molecular traps to better bind target molecules have been explored, but they have added complexity to the material synthesis and tend to produce background signals that complicate data analysis.

In the paper, Vikesland describes a study he and Wei conducted using bacterial cellulose as a SERS platform created by synthesizing nanocomposites made of bacterial cellulose interlaced with gold nanoparticles. Bacterial cellulose makes an excellent base for a SERS substrate. It is low-cost and easily fabricated, and its fibers are nanoscale in diameter and retain their 3-D structure in water.

The study used this platform to attempt to detect a number of common pollutants — carbamazepine, atrazine, and melamine, among others. By manipulating the suspension pH, the authors were able to consistently and reproducibly increase the SERS signal due to the increased affinity for the pollutant to the substrate at low pH.

A SERS platform based on bacterial cellulose could finally help fulfill the promise of this exciting technology. The platform can be synthesized in a one-step process and it can be reused many times. The protocol could simplify and reduce the cost of detecting many compounds. The platform is easy and cheap to synthesize and provides short sampling and detection times.

Vikesland also leads an international team of researchers as the principal investigator for a five-year $3.6 million Partnerships in International Research and Education grant from the National Science Foundation. They seek to halt wastewater-derived antimicrobial resistance dissemination.